Image display apparatus containing an image entry function allowing the user to enter information by touching the screen with fingers (hereafter simply called touch) are used in portable terminals such as PDA, and customer guidance terminals such as automated reception terminals. Image display apparatus containing this type of image entry functions utilize known methods including a method that detects the change in resistance in the (screen) section that was pressed, a method to detect the change in capacitance in the pressed section, and a method to detect the change in light in the section where the light was blocked when touched.
In recent years, methods are being developed in particular for detecting the coordinates of the section that was touched by the change in the amount of external light in the pixel structure forming the screen. An apparatus including thin film transistors (TFT) and light sensing elements (photo sensors) formed in pixels on the liquid crystal display panel serving as the liquid crystal display apparatus is disclosed for example in patent document 1.
FIG. 15 is a concept view for describing the pixel structure in an image display apparatus of the related art with the image entry function formed from photo sensors within the pixel. An image display apparatus 2 in the figure is a liquid crystal display panel containing photo sensors (third photo sensor, not shown in drawing) within the pixels. A reference photo sensor PSA (first photo sensor) is installed at the upper end within display region 16 of image display apparatus 2. Also, a reference photo sensor PSB (second photo sensor) is installed outside the display range 16 of image display apparatus 2. The first photo sensor detects backlight and light (external light) irradiated from the observation surface side. The second photo sensor is shielded from light irradiated from the observation surface side, but detects the backlight.
The technology of the related art in other words, includes a first photo sensor for detecting external light and light from a backlight; and a second photo sensor for detecting only light from the backlight and shielded from external light; and a third photo sensor for receiving external light and backlight and using light from the user's touch. The related art further includes a signal scanner unit for receiving and processing the first, second, third sensitivity signals from the first, second, third photo sensors; and a signal processor unit for adjusting the sensitivity signals of the third photo sensor based on the first and second sensitivity signals processed in the signal scanner unit. The technology of the related art can in this way judge the contact (touch) information received from the user touching the screen, even if the external environment changes, by utilizing sensitivity signals from the first photo sensor and the second photo sensor to adjust the third photo sensor.
FIG. 16 is an equivalent circuit diagram for describing the pixel structure for an image display apparatus of the related art with an image entry function made up of photo sensors as pixels. This image display apparatus utilizes a liquid crystal display panel and is disclosed in JP-A No. 2005-129948 as follows. The image display apparatus with liquid crystal display panel includes multiple gate lines (GL), multiple data lines (DL), a first switching element (Q1) electrically connected to a gate line and data line, and a first storage capacitor (holding capacitor, CST1) and a liquid crystal CLC connected to the first switching element (Q1). The apparatus further includes a first voltage line (VL1), a second voltage line (VL2), a second switching element (TS1) for detecting the intensity of the external light L and converting it to an electrical current, a second storage capacitor (CST2) for retaining the charge formed by the electrical current provided from the second switching element (TS1), and a readout line (R) and a third switching element (TS2) for outputting the charge stored in the second storage capacitor (CST2). The second switching element (TS1), second storage capacitor (CST2) and third switching element (TS2) together form one type of photo sensing unit.